The fundamental steps of processing color photographic light-sensitive materials generally include a color developing step and a silver removing (i.e., a desilvering) step. Thus, an exposed silver halide color photographic material is introduced into a color developing step, where silver halide is reduced with a color developing agent to produce silver and the oxidized color developing agent in turn reacts with a color former to yield a dye image. Subsequently, the color photographic material is introduced into a silver removing step, where silver produced in the preceding step is oxidized with an oxidizing agent (usually called a bleaching agent), and dissolved away with a silver ion complexing agent usually called a fixing agent. Therefore, only a dye image is formed in the thus-processed photographic material. In addition to the above described two fundamental steps of color development and silver removal, actual development processing involves auxiliary steps for maintaining the photographic and physical quality of the resulting image or for improving the preservability of the image. For example, such processes include a hardening bath for preventing a light-sensitive layer from being excessively softened during photographic processing, a stopping bath for effectively stopping the developing reaction, an image stabilizing bath for stabilizing the image, and a layer removing bath for removing the backing layer on the support.
The above described silver removal step may be conducted in two ways: one uses two steps employing a bleaching bath and a fixing bath; and the other is more simple and is conducted in one step employing a bleach-fixing bath containing both a bleaching agent and a fixing agent for the purpose of accelerating the processing and labor elimination.
In recent years, bleach processing using a ferric ion complex salt (e.g., aminopolycarboxylic acid-ferric ion complex salt, particularly iron (III) ethylenediaminetetraacetate complex salt) as a major bleach bath component has mainly been employed in processing color photographic light-sensitive materials in view of the acceleration and simplification of the bleaching provided and the need for preventing environmental pollution.
However, ferric ion complex salts have a comparatively low oxidizing power and, therefore, have insufficient bleaching ability.
In order to raise the bleaching ability of a bleaching solution or a bleach-fixing solution containing a ferric ion complex salt such as iron (III) ethylenediaminetetraacetate as a bleaching agent, it has been proposed to add various bleach accelerating agents to the processing bath.
Examples of such bleach accelerating agents include 5-membered heterocyclic mercapto compounds as described in British Patent 1,138,842, thiadiazole derivatives as described in Swiss Patent 336,257, thiourea derivatives, and thiazole derivatives, etc. However, these compounds do not necessarily have sufficient bleach accelerating effects when they are added to a bleaching solution or a prebath thereof. Also, insufficient bleach accelerating effects are obtained when they are added to a bleach-fixing solution or a prebath thereof. Further, in the latter case they react with silver ions present in the bleach-fixing solution to form a precipitate which creates many troubles. For example, the precipitate can block filters of a circulation system in an automatic processing machine, and it adheres to photographic light-sensitive materials, resulting in stain formation.
A processing method is also known wherein a 5-membered heterocyclic compound containing two or three nitrogen atoms as ring constituting members and having at least one mercapto group is added to a bath just before a bath of the bleaching processing as described in JP-A-54-52534 (the term "JP-A-" as used herein means an "unexamined published Japanese patent application"). However, when these compounds are directly added to a bleaching solution or a bleach-fixing solution, sufficient bleach accelerating effects cannot be obtained. In addition, they lack stability in the processing solution and cannot endure use for a long period of time.
Furthermore, heterocyclic alkylmercaptan derivatives as described in JP-A-53-32736, disulfide compounds as described in JP-A-53-95630, isothiourea derivatives as described in Research Disclosure, No. 15704 (May, 1977), and aminoalkylmercaptan derivatives as described in U.S. Pat. No. 3,893,858 are known as bleach accelerating agents. However, these bleach accelerating agents have various disadvantages, although some of them show a satisfactory bleach accelerating effect. More specifically, when these compounds are added to a bleaching solution and color photographic materials are continuously processed using such a bleaching solution, precipitate occurs in the bleaching solution, which causes many difficulties. The precipitate clogs filters of a circulation system in an automatic processing machine and adheres to photographic light-sensitive materials, resulting in stain formation. Further, it is also known that the bleach accelerating effect is reduced under running conditions. This is believed to be due to the fact that thiol or disulfide is converted to a thiolsulfonate ion by a sulfite ion which is carried over from a developing solution into a bleaching solution and thus loses its adsorbing ability to developed silver.
Therefore, in order to effectively accelerate silver removal, it has been proposed to incorporate such a bleach accelerating agent into a silver halide color photographic material instead of adding the compound to a processing bath such as a bleaching bath or a bleach-fixing bath. However, many compounds which are generally designated bleach accelerating agents form undesired fog when they are directly incorporated into color photographic light-sensitive materials. Moreover, they cause decrease in sensitivity and change in photographic characteristics (such as sensitivity, gradation, fog, etc.) and can not be practically employed.
Many attempts have been made to overcome such problems as fog formation caused by the incorporation of bleach accelerating agent into a color photographic light-sensitive material and to further increase the bleach accelerating effect. For instance, there is a method of using a bleach accelerating agent in the form of a salt (for example, a silver salt, etc.) with a heavy metal ion as described in JP-A-53-134430, JP-A-53-147529 and JP-A-55-64237. However, this method does not provide a sufficient bleach accelerating effect. Also, methods utilizing a bleach accelerator releasing coupler are described in Research Disclosure, No. 11449 (1973) and JP-A-61-201247. However, these known bleach accelerator releasing couplers can release bleach accelerating agents only at color development and do not release them at the time of bleaching or bleach-fixing, and thus their bleach accelerating effects are still unsatisfactory. Further improvement, accordingly, has been desired.